One self-evident fact in the grand narrative of Los Alamos National Laboratory has to do with its role in making the weapon that brought an end to World War II.

But that world-saving assumption, so rarely examined because it’s so obvious, was roughed up last week by a revisionist historian who mounted an assault on a vulnerable piece of conventional thinking.

Independent scholar Ward Wilson, who spoke at a meeting of the Los Alamos Committee on Arms Control and International Security, was careful to say that he was not arguing about the morality of the bomb or the bombing, that is, whether the attack could have or should have been avoided, doubts that began to surface in the ’60s.

Wilson’s concern rather marks a more recent interpretation of the question that began in the ’90s with new documents from the archives of the three powers involved – the Japanese, the Soviets and the U.S. This newer debate asks whether the atomic bomb was an effective weapon.

Was it, Wilson asked in his talk, a truly useful weapon, like the newly forged iron weapons that enabled the Assyrian ascendancy in the Middle East from 700-500 B.C.E.? Was its impact on the order of the reflex bow that armed the Mongols’ 13th-century conquest of greatest swath of land in the history of the world?

Or was it the other kind of weapon in the annals of history: significant and notable, like the chariot of ancient times, or more recently, chemical weapons? Both innovations surely inflicted horror, but they turned out to be, for one reason or another, difficult to use.

The first atomic weapon ever used against an enemy in war was dropped Aug. 6, 1945, on Hiroshima. A second atomic bomb, and the last ever to be so used, fell on the city of Nagasaki two days later.

Do they amount to a sufficient explanation for the surrender of the Japanese four days later?

When John Hopkins, a former senior official at the laboratory gave a talk in Los Alamos last month about the use of nuclear weapons during World War II, he expressed as his bottom line, “that nuclear weapons were essential to ending World War II, before a planned U.S. invasion of the home islands.”

Countering Japanese explanations at the time, Wilson argued, “They lied.”

It was a face-saving excuse, he said – whereas Wilson decodes the Americans’ playing up the efficacy of atomic weapons as a useful deterrent against the soviets before the arms race began in full.

“If our genius did it, great. If the Soviets did it, it is no credit to us,” Wilson said.

As for an alternative cause, he agrees with other historians who have argued that the Soviet intervention from Manchuria Aug. 9 “touched off a crisis” that went beyond the nuclear weapons.

In his analysis, Wilson cites conversations between senior military officials as one indication that atomic attacks were not “the center of the conversation.”

Finally, Wilson, both in his talk and in his paper, brings up the problem of aerial bombing of cities and the numerous examples – from the German bombing of London and the Allied bombing of German cities earlier in the war, to the American bombing of Hanoi more than two decades later – that they didn’t result in surrender.

In terms of scale and even in terms of deaths and destruction, the atomic bombing of Hiroshima was not so different from the long campaign of American air attacks against 68 Japanese cities that had begun in March 1945, Wilson said.

“The problem with the bomb is that it is difficult to distinguish a single drop of rain in the midst of a thunderstorm,” he said, noting that from July 16 until those first days of August, eight of 25 Japanese cities were destroyed as completely or more completely than Hiroshima with conventional bombs.

Hopkins, who said he was unable to attend Wilson’s talk, said that Japanese scientists had thought the atomic bomb could not be made and that after Hiroshima, there was probably only one – until the strike on Nagasaki.

They recognized the new weapon meant that one plane could the firepower that had devastated the other cities, Hopkins said.

“The Russian invasion was not a shock,” Hopkins said. “It was a disappointment, but not a shock in the sense that the nuclear weapons were a shock.”

Although the talk was followed by the usual vigorous discussion by the arms control group, there was little debate about the details of the historical interpretation.

Wilson said in an e-mail after his talk that he was “absolutely surprised that people didn’t object more.”

He added, “The whole notion that Hiroshima didn’t win the war tends to be sort of preposterous until you’re assaulted by the full force of the entire presentation.”